The Background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present disclosure.
Referring now to FIG. 1, first and second network devices 10 and 12 include network interfaces 14 and 16, respectively, each with physical layer devices (PHYs) 18 and 20, respectively. The PHYs 18, 20 communicate with a medium 19 such as cable including twisted pairs of wire. The PHYs 18, 20 communicate with media access control devices (MACs), 19, 21, respectively, which provide an interface between the PHYs 18, and the network devices 10, 12, respectively. The PHYs 18, 20 also include respective transmitters and receivers that are collectively identified at 22, 24. The PHYs 18, 20 include autonegotiation modules 26, 28, respectively. As can be appreciated, the autonegotiation modules 26, 28 may be disabled; and/or the PHYs 18, 20 may be operated in forced 10 Mb/s or 100 Mb/s modes. The autonegotiation modules 26, 28 may be disabled during debug and/or troubleshooting to reduce system complexity.
There are different Ethernet networking standards having different data rates. 1000BASE-T has a maximum data rate of 1 Gb/s. 100BASE-TX has a maximum data rate of 100 Mb/s. 10BASE-T has a maximum data rate of 10 Mb/s. When two network devices communicate, they preferably communicate at the highest common speed. The procedure for negotiating the communication speed and/or other connection details is called autonegotiation. Further details concerning autonegotiation are also set forth in IEEE section 802.3, which is hereby incorporated by reference in its entirety.
Referring now to FIG. 2, a simplified state diagram corresponding to FIG. 28-16 of IEEE section 802.3 is shown. Generally, a local network device and a remote link partner advertise their abilities before establishing a link. The two network devices then select modes of operation that are shared. During autonegotiation, a network device may transition through states 76→78→80→82→84→86→82→84→88→94 in FIG. 2. State 90 is associated with an autonegotiation wait timer that typically has a period between 500 ms and 1000 ms. If the link drops out, the autonegotiation state machine transitions from state 90 to state 92 and returns to the initial state in state 80.